Ayman A. Diab

Identification of drought-inducible genes and differentially expressed sequence tags in barley

Drought limits cereal yields in several regions of the world and plant water status plays an important role in tolerance to drought. To investigate and understand the genetic and physiological basis of drought tolerance in barley, differentially expressed sequence tags (dESTs) and candidate genes for the drought response were mapped in a population of 167 F8 recombinant inbred lines derived from a cross between “Tadmor” (drought tolerant) and “Er/Apm” (adapted only to specific dry environments). One hundred sequenced probes from two cDNA libraries previously constructed from drought-stressed barley (Hordeum vulgare L., var. Tokak) plants and 12 candidate genes were surveyed for polymorphism, and 33 loci were added to a previously published map. Composite interval mapping was used to identify quantitative trait loci (QTL) associated with drought tolerance including leaf relative water content, leaf osmotic potential, osmotic potential at full turgor, water-soluble carbohydrate concentration, osmotic adjustment, and carbon isotope discrimination. A total of 68 QTLs with a limit of detection score ≥2.5 were detected for the traits evaluated under two water treatments and the two traits calculated from both treatments. The number of QTLs identified for each trait varied from one to 12, indicating that the genome contains multiple genes affecting different traits. Two candidate genes and ten differentially expressed sequences were associated with QTLs for drought tolerance traits.

Molecular cloning, expression, sequence analysis and in silico comparative mapping of trehalose 6-phosphate gene from Egyptian durum wheat

Trehalose is a non-reducing disaccharide which consists of two glucose units that functions as a compatible solute to stabilize the membrane structures under heat and desiccation stress. Trehalose-6phosphate synthase (TPS) and trehalose-6phosphate phosphatase (TPP) are the key enzymes for trehalose biosynthesize in the plant kingdom. On the basis of bioinformatics prediction, fragment containing an open reading frame of 945 bp was cloned from durum wheat. Sequence comparison and analysis of conserved domains revealed the presence of a TPP domain. Full length of the gene was isolated using gene race technology. Semi-quantitative RT-PCR and real time quantitative PCR indicated that the expression of this gene is up-regulated in response to drought stress. The biochemical assay of the trehalase activity showed that the enzymes activity decreased under the dehydration stress. The obtained phylogenic tree showed that the isolated TPP protein forms a distinct clad close to the Oryza sativa trehalose-6phosphate phosphatase. In silico and comparative mapping indicated that the isolated TPP gene is localized on rice chromosome 8, durum wheat chromosome 20, bread wheat chromosome 3B, oat linkage group E, sorghum chromosome 4 and barley 5H.